After thirty years away, Met detective DI Ruth Calder returns to Shetland on the trail of Ellen Quinn – the scared witness to a London gangland murder. In Lerwick, Tosh pauses her investigation into a string of sinister animal deaths to help Calder find Ellen before it's too late.Ellen's family are the influential and notorious Bains, led by dominant matriarch, Grace. Calder and Tosh discover her mother Stella and father Kieran haven't seen Ellen since she left for London six months ago and are surprised to hear that she's back in Shetland.Matters are made worse when armed London gangsters - the experienced Howell and volatile Nowak - arrive on the Isles on a mission to silence Ellen.On top of the twists and turns of the case, Calder is faced with figures from her past including her ex-boyfriend Cal Innes and estranged younger brother Alan – now the minister of their late father's old church. However, these siblings have starkly different views of their shared childhood.As the case gathers momentum, Calder and Tosh are stunned by news of a brutal murder which has all the hallmarks of organised crime. However, there's another shock in store for the team.